A complex recombination pattern in the genome of allotetraploid Brassica napus as revealed by a high-density genetic map.

Guangqin Cai,Jacqueline Batley,Qingyong Yang,David Edwards,Bin Yi,Chuchuan Fan,Yongming Zhou,Hector Candela

doi:10.1371/journal.pone.0109910

Guangqin Cai, Jacqueline Batley + Show 6 more

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https://doi.org/10.1371/journal.pone.0109910

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Abstract

Polyploidy plays a crucial role in plant evolution. Brassica napus (2n = 38, AACC), the most important oil crop in the Brassica genus, is an allotetraploid that originated through natural doubling of chromosomes after the hybridization of its progenitor species, B. rapa (2n = 20, AA) and B. oleracea (2n = 18, CC). A better understanding of the evolutionary relationship between B. napus and B. rapa, B. oleracea, as well as Arabidopsis, which has a common ancestor with these three species, will provide valuable information about the generation and evolution of allopolyploidy. Based on a high-density genetic map with single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers, we performed a comparative genomic analysis of B. napus with Arabidopsis and its progenitor species B. rapa and B. oleracea. Based on the collinear relationship of B. rapa and B. oleracea in the B. napus genetic map, the B. napus genome was found to consist of 70.1% of the skeleton components of the chromosomes of B. rapa and B. oleracea, with 17.7% of sequences derived from reciprocal translocation between homoeologous chromosomes between the A- and C-genome and 3.6% of sequences derived from reciprocal translocation between non-homologous chromosomes at both intra- and inter-genomic levels. The current study thus provides insights into the formation and evolution of the allotetraploid B. napus genome, which will allow for more accurate transfer of genomic information from B. rapa, B. oleracea and Arabidopsis to B. napus.

Highlights

Polyploidy plays a crucial role in plant evolution [1,2,3]
Based on the above analysis, we further identified homoeologous collinear fragments of B. rapa and B. oleracea in the B. napus genome using a similar method described by Parkin et al [18]
To distinguish the origins of translocation events in B. napus genome, we considered the reciprocal translocations occurred between the homoeologous chromosomes of the A-genome and C-genome [18]

Summary

Introduction

Polyploidy plays a crucial role in plant evolution [1,2,3]. Most flowering plants, including the majority of agricultural crops, are polyploid [2,4]. B. oleracea (CC, 2n = 2x = 18), and three amphidiploid species derived from the three diploids, B. napus (AACC, 2n = 4x = 38), B. juncea (AABB, 2n = 4x = 36), and B. carinata (BBCC, 2n = 2x = 34) [10]. B. napus, as the most important oil crop among the six species in the U-triangle, is estimated to have been generated 5,000 to 10,000 years ago by the natural hybridization of its two progenitor diploids, B. rapa and B. oleracea [11,12].

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